Current supply circuits



Nov. 24, 1931. v D. F. WHITING 1,832,836

- CURRENT SUPPLY CIRCUITS Filed April 1'7, 9

lnvenfar Liana/d F W/I/f/hy Patented Nov. 24, 1931 can srarss PATENTorrice ONA D F. wmrme, or'ron'r wAsi-rr'iie'ron, YORK'ASSIGNOR 'ro BELLTELE- PHONE LABORATORIES, INCORPORATED, OF NEW YORK, Y., A CORPORATIONOF ew YORK Application filed A ri 17 1 This invention relatesto Currentsupply 'The rectifying system may employ any suitable type of rectifier,such as a vacuumtube,

chemical or mechanical rectifier.

A further object of the invention is lLO'iIlsure that the low potentialrectified current supply,i which may be utilized for any desired purposeprovides a voltage always less than a prescribed maximum above groundunder the various contingencies of operation of the system.

V In energy supply sets, such as those furnishing operating'current tovacuum' tube amplifiers and the like, voltagesamounting to severalhundred volts are often encountered. Frequentl the system in which thehigh voltage apparatusis used, requires also relatively low voltages andit is economical and convenient to obtain all suchpotentials p from thesame supply set. Inorder to guard against dangers from the highoperating voltages, it is customary to include in one casing all of theapparatus utilizing the high voltages, However, if a low potentialsupplyis to be derived from the supply set,'it is often desirable to bringoutleads, and it then becomes important to insure that the voltages ofthese exposed leads cannever rise above the predetermined maximum inorder that thesafety of the operator and apparatus may not beendangered.

Theinvention provides low-Voltage connections to a high voltage supply,which insures that the potential on the supply leads will not risehigher than the predetermined maximum above ground.

Inone embodiment of the: invention a resistance element is placed in thepath of the rectified current supplied by the rectifier.' The lowvoltage'supply leads are bridged across this resistance element, oneterminal ofwhich is grounded or is maintained at al low potentialwith'respect to ground, furnishing a. direct current supply, the voltageof, which is determinedby the'v'alues ofthe rectiounnnnrr suPrnYCIRCUITS 1926, Serial no. 102,644.

tied currents flowing throughthe resistance element and the resistanceof the external circuit'bridgedacross it. A definite maximum voltagebetween the external wires canvbe easily predetermined from the value.of the current which flows when the external circuit is opened, andthevalue of the internal resistance element. It oneterminal of thisresistance element s grounded, the potential between the external leadconnected to the opposite terminal and ground is never higher than thedrop of potential across this resist ance. Ii": one terminal of theresistance is maintained at a low potential with respect to ground, thehighest potential above ground which the other wire can assume is thealgebraic sum or the potential of the first wire and the difference ofpotential between the wires.

Oneof the systemswliich has been chosen to illustratethe operation ofthe invention is a radio receiving set comprising a rectifieramplifierunit and'aseparate detector'unit, the detector unitbeing supplied withlow voltage from-the rectifier for theplate and filament of'the detectortube. The other system is a speechamplifier system, such [as V a publicaddress set comprising the same rectifier-amplifier unitas in the radioreceiving set with the add tion of a microphone which is supplied withoperating current from the rectifier system in accordance with thisinvention. Y Y

Referring to'the drawings, Fig. l is a schematic drawing of theradioreceiving system i and a v Fig. 2 is a partial schematic drawing showmgthe speech amplifier set referred to.

referred to above as an illustrative example,

lines) any well known type of radio intercepting and detectingrsystem,the one shown comprising an aerial'6, a coupling coil 7, a variabletunlng condenser. 8 and a vacuum tube'9." Y 9 w The rectifier-amplifierunit inclosedinthe In Fig. 1 the rectifier-amplifier unit is metal case4 comprises a transformer 14 equipped with terminals on its primarywinding to which an external source ofalternating current 11 may beconnected. The transformer 14 has a secondary winding 15 supplyingfilament heating current to an amplifier tube 16, a secondary winding 18supplying filment current to the rectifier tube 13, and a secondarywinding 19 supplying the high op erating voltages for the system. Afilter arrangement for the purpose of smoothing out the ripples in therectified current may be composed of a condenser 20 and a retardationcoil 21 or it may consist of several such coir densers and retardationcoils, only those mentioned being shown in the sketch for the pur poseof simplification.

Signals to be amplified are impressed on a tube 23 romprising the firststage of audio frequency amplification through an input t 'ansformer 24and on a second stage of audio frequency amplification including tube 16through a transformer 25. The output energy of this unit is availableand is supplied through an output transformer 26 to a receiver or otherload device. Resistances 28 and 29 of approximately 100,000 and 50,000ohms respectively, acting in conjunction with condensers 31 and 32respectively, aid in providing the necessary grid bias for the tubes 23and 16, without disturbance caused by their connection to the rectifiedcircuit or to the plate supply system Condensers 33 and 34 serve toreduce the disturbing effets in the plate circuits of tubes 23 and 16,respectively, caused by their connection to the rectified circuit, whilealso serving as by-pass condensers for the higher frequency waves whichpass through the amplifying tubes. A condenser 35 likewise provides anadditional filter element to the circuit furnishing the plate voltage tothe detector tube and ate as a return circuit for the alternatingcurrent flowing in the detector plate circuit.

The resistance composed of elements numbered to 46 inclusive, with thevarious connections forms a distribution network for supplying variousvoltages to the elements of the system. The rectifier circuit beginningat the cathode of the rectifier tube 13 is through secondary 19, retardcoil 21, to the terminal of resistance element 40 where it branches, onecircuit tracing through the primary winding of transformer 26 to theanode of tube 16, to the filament of tube 16, to the mid-point ofsecondary winding 15 and thence to the point the other circuit tracingthrough resistance elements 40, 41 and 42 to the point 50. From point 50the circuit passes through the filament of amplifier tube 23, to aterminal 56, through the filament of detector tube 9 to a terminal 57,through resistance units 45 and 46 to the anode of rectifier tube 13.Connected in shunt to the filaments of tubes 23 and 9 are resistanceelements 43 and 44, respectively. In addition to the circuits justtraced portions of the rectified current flow from the junctions ofresistance units 4041 and 40-42 through conductors 51 and 52 and theprimary windings of transformers 25 and 24 to the plates of tubes 23 and9, respectively.

In the circuits just traced in the foregoing paragraph it is seen thatthe resistance units 40, 41 and 42 form a shunt across the s )ace of theamplifier tube 16, protecting c onr cheers 20 and 34 from abnormalincreases in voltage if the tube 16 should become inoperative due to itsfilament burning out or if it is removed from its socket. Similarlyacross the space path of the tube 23 are shunted resistance units 41 and42 by leads 51 and 53 providing protection to condenser 33 if the tube23 becomes inoperative due to its filament burning out or removal of thetube. The proper amount of plate voltage is determined by the value ofthe resistance units just mentioned and the respective currents throughthem. The resistance units 42, 43 and 44 serve the same function withrespect to condenser in the operation of detector tube 9. The platerircuit for this tube is from the junction point between resistanceunits 41 and 42 through conductor 52, terminals and 59, primary windingof transformer 24, terminal 58 and thence to the plate.

The in aximum open line potential between either of terminals 58, or 60and the terminal 57 may be determined by the various currents flowingthrough the elements 42, 43 and 44 when the circuit to the plate of tube9 is opened. The voltage between the terminals 56 and 57 on open circuitis determined by the current through resistance unit 44 under thiscondition. The open circuit voltages may be thus predetermined andkeptbel'ow a prescribed maximum, in accordance with the invention. Theapproximate values of the resistances above mentioned are as follows:unit 40, 4000 ohms; unit 41, 700 ohms; unit 42, 700 ohms; unit 43, 1500ohms: and unit 44, 1500 ohms. I

Since the filaments of tubes 9 and are connected in series and havesimilar resistance values and since there is shunted across them theresi tance units and 44 of equal resistance value, mentioned. above, thefour resistai'ices form a bridge and conductor connected between thejunction points of the two filaments and the junction point of the tworesistances and 4 will normally have no current fiowin 'n it. Thisconductor is of advantage, b .vcr, in limiting the voltage between to-56 and 5? when the radio detector or other apparatus used, which will bedescribed hereinafter, is d' connected from the ranplifier. A resis 54,having a value equal to the filament 1 anceof tube 9, is connected atone end to terminal 57 and is provided at the other end s (i do wasdisconnected from the unit. Terminal 57 is the ground terminal and isconnected to the metal case at the point 5. The terminals 58 and 59 arethe terminals of the input coil 24; and terminal 60 is the voltageterminal operating at a higher. potential than the terminal 56 and, inthis particular circuit, it is used to 'supplythe plate potential todetector tube9. These terminals are the only supply connections leadingfrom the rectifier-amplifier unit, and in this manner, several sourcesof relatively low voltages may be provided whichmaybe handled withoutendangering life or apparatus.

The resistance elements and 46 of the potentiometer-dike arrangement arefor the purpose of supplying proper values'of negative biasingpotentials for the grids of amw pliiier tubes 23 and 16 and may haveohmic resistances of approximately and 300 ohms, respectively. p I

Fig. 2 is drawn to show a similar rectifierampiifier set enclosed in themetal case 4 as shown in Fig. l with a microphone unit associatedtherewith both units comprising a speech amplifier system. A microphone63 is supplied with operating current througha retardation coil 64 andthe lead 53, the lead being bridged across the single iesistance unit el, using terminals 56. and 57 corresponding to the same numberedterminals in Fig. 1: Assuming that the microphone 63 operates on alowervalue of current than the filament of tube 9 in Fig. 1, lead 53 isutilized to return a. current whichfis the difference betweenthe currentpreviously taken by the filament of tube 9 and the current now taken bythe microphone 68. The alternating current output of the microphone isimpressed upon the input transformer at terminals 58 and 59 similar tothe arrangement described in connection with Fig. l. The terminal :57 isgrounded and connected'to the metal casing l at the point 5 so that thevoltage across the terminals 56 and 57 or ground will never be greaterthan the product of the current in the resistance element 44 when themicrophone is disconnected from the rectifieramplifier set andthe valueof the resistance element itself. For the purpose of the presentdisclosure and in accordance with experience a potential'of 200 volts istaken as a maximum voltage on external leads from the standpoint ofpersonalsafety and fire hazards. In the circuits operated by applicantthe maximum voltage of the external vleads never reachedlOOvolts. V r LThis invention has been described in con-.

nection with a particular single tube circuit 7 of less than a but isnot limited :to this type of rectifieror these circuits but only by thescope of the 7 attached claims. What is claimedis: a

1. In a current supply system,a high voltage portion comprising arectifier and apparatusutihzing rectified high voltage, a protectingcasing enclosing said high voltage portion, means maintaining saidcasing at substantially ground potential, a resistance includedin thepath of the rectified current, one'terininal of'said resistance beingconnected toground, and a lead connected to a point on resistance, theamount of resistance included between the ground and said point ofconnection being of sucha value that the drop of potential across it ismany times smaller thanthe maximum operating voltage of said system,said lead extending outside of said casing for supplying direct currentpredetermined maximum potential. p p I a 2. Ina current supply system, asource of alternating current potential, a rectifier, a

main load circuit receiving current from said rectifier at a. highpotential, a resistance element in the path of the rectified current, aprotecting casingyenclosing all of said elements connections from saidresistance external to saidcasing for'supplying direct current voltageto an auxiliary load circuit available to an operator, one terminal ofsaid resistance beinggrounded, the amount of resistance included betweensaid connections and ground being such that the'voltage be: tweeneitherof said connections and ground is less than a prescribed maximumpotential. "3. In a current" supply system, a source of alternatingcurrent potential, a rectifier, a

main load circuit receiving current therefrom at a potential of a higherorder of magnitude than 200 volts, a resistance element in the path ofthe rectified current, one terminal of which is grounded, a protectingcasing enclosing allofsaidelements,saidcasingbeing grounded, connectionsfor shunting an auxiliary load circuit external to said supply setacross said resistance element, whereby the said auxiliary work circuitreceives a portion I of the reitified current, the amount of resistanceincluded between sald connections being such that the potential betweeneither of said connections and ground is always as low as 200 volts. i V4. In a high voltage energy supply system, a cabinet, a rectifier, ahigh voltage load circuit utilizing a voltage in excess of 200 volts, aresistance in the path of the rectified cur rent, one terminal of whichis substantially at ground potential, said rectifier, load circuit andresistance being enclosed within said cabinet, said resistance havingleads therefromexternal to said cabinetfor the purpose j of'supplying alow uni-directional potential many times smaller than that furnishedsaid load circuit internal to said cabinet, the point of connection ofsaid ground to the circuit and. the magnitude of said resistance beingsuch that said potential Will always be less 5 than a value ofapproximately 200 volts.

5. In combination, a microphonic transmitter, an audio-frequencyamplifier connected therewith, and an energizing circuit for themicrophone in series with the plate cir- 1 cuit oi? the amplifier.

6. In combination, a microphonic transmitter, an audio-frequencyamplifier connected therewith, and an energizing circuit for themicrophone in series with the plate circuit oi the amplifier and asubstantial series resistance.

7. In combination, a microphonic transmitter an audioirequnecy amplifierconnected therewith, and an energizing circuit for the 20 microphone inseries with the plate circuit or the amplifier and a resistance of theorder of 1000 ohms.

8. 131 combination, a microphonic transmitter, an audio-frequencyamplifier connected therewith, an energizing circuit for the microphonein series with the plate circuit of the amplifier and a substantialseries resist ance, an d a resistance bridged across the terminals ofthe energizing circuit from the 30 a .ipliiier.

9. In combination, a microphonic transmitter, an audio-frequencyamplifier connected therewith, an energizing circuit for then'iicrophone in series with the plate circuit of the amplifier and asubstantial series resistance, and a lay-passing condenser for the saidresistance.

In witness whereof, I hereunto subscribe my name this 5th day of April,A. D. 1926. DONALD F. l/VHITIINGr.

